Centrifugal pumps transport fluid by converting input rotational energy to hydrodynamic energy. The energy conversion is provided by an impeller driven by an engine. Fluid enters the impeller inlet along an axis parallel to the pump's drive shaft. The disc-like impeller reduces liquid pressure at the eye which draws in more fluid and centrifugally accelerates the fluid into a radial pump outlet. Centrifugal pumps are commonly used to transport fluids containing solid particles, referred to as “slurries.”
Because of the naturally high dynamic loading and hydraulic pressures inherent in centrifugal pumps, and attendant maintenance and installation requirements, a variety of seals are employed. The variety of seals attempt to balance the need to prevent undesirable fluid leaking or air ingestion during pumping operations while allowing ease of installation and maintenance. Ideally, the configuration of seals allows predictable containment and control of the fluid within the pump under varying hydraulic pressures and rotational speeds. In addressing the above engineering and operational requirements, centrifugal pumps may include a dynamically-actuated seal to automatically engage or increase sealing capabilities as a function of impeller or drive shaft rotational speed. It is desirable that any dynamically-actuated pump sealing elements require minimal lengthening of the drive shaft and are easily and predictably installed.
One example of a centrifugal pump fitted with a dynamically-actuated seal is disclosed in U.S. Pat. No. 5,667,356 to Whittier et al (“Whittier”), incorporated herein by reference in its entirety. The centrifugal pump incorporates a ball bearing assembly as a force-responsive governor to control opening and closing of a fluid path leading from an expeller region into a seal. The seals are composed of hard, low-friction sealing materials for handling acids and of resilient materials for handling slurries owing to the solids content in the slurries. The force-responsive governor of Whittier is limited in its operational range once installed due to the self-confined design that requires disassembly to adjust the number of governor balls. Also, Whittier's seals do not lend to predictable containment and control of the fluid of the pump due to lack of adjustment for compounded tolerances.
Another example of a centrifugal pump fitted with a dynamically-actuated seal is disclosed in U.K. Patent Application No. GB 2,078,877 to Waters (“Waters”), incorporated herein by reference in its entirety. The centrifugal pump of Waters has a drive shaft rotating a pumping impeller and an axially adjacent impeller providing a dynamic seal for a pump chamber. A partition separates the dynamic seal from a static seal comprising a carbon ring on a carrier on the shaft spring pressed against a stationary ring secured to the partition. As illustrated in FIG. 1 of Waters, the carrier is axially moved by centrifugally acting arms (58) to withdraw the sealing ring when a predetermined shaft speed is exceeded. The force-responsive seal of Waters, as provided by the centrifugally acting arms, present an unnecessarily large footprint due to an extended axial length of the shaft to accommodate the axially aligned arms. Lengthening a drive shaft is more costly, creates a heavier shaft requiring more robust bearings adding further expense, and increases vibration and noise. In addition, the orientation of the arms parallel to the shaft create a hazard for operators working in the vicinity of the arms during operation. A hand, arm or tool placed in the path of the rotating arms would likely be damaged and could also cause damage to the pump. Furthermore, Waters' seals do not provide predictable calibration and initialization of the pump under varying hydraulic pressures and rotational speeds.
A further issue with cartridge seals generally is the use of removable pre-load tabs. FIG. 1 is an illustration of one example of pre-load tabs applied to a cartridge seal. As shown, the tabs secure the shaft sleeve to the cartridge housing and apply a pre-load to the seal. Once the cartridge seal is installed, the tabs must be removed for the pump to operate as the shaft sleeve must be free to rotate with the pump shaft. However, the tabs must be reinstalled for maintenance and adjustment of the cartridge seal. Therefore, the tabs must be saved and stored in a known and reliable location for use during future maintenance. As can be appreciated, the tabs are often misplaced, lost or even thrown away.
There is a need for a pump fitted with a sealing system that prevents undesirable fluid leaking or air ingestion. There is a need to provide a centrifugal pump with a dynamically-actuated seal that automatically increases sealing capabilities as a function of impeller or engine drive shaft rotational speed. There is a further need to provide a dynamically actuated seal in a manner that reduces overall seal axial length and that presents a minimal profile when actuated. In addition, there is also a need for a cartridge sealing system for use with pumps that provides ease of installation and maintenance, as wells as predictable containment and control of the fluid within the pump under varying hydraulic pressures and rotational speeds. There is a need for a system and method to apply a preload to a cartridge seal without removable tabs. The present invention meets these needs by providing both an improved governor actuated seal and a cartridge seal that provides a method of and apparatus for attaching a cartridge seal to a pump.